M. E. Hopkins and J. A. Simon
The McCormick Group (Kosanke et al., 1960, p. 28) is named for McCormick in northwestern Pope County, where the various units of this group are prominently exposed.
Extent and Thickness
The McCormick Group in Illinois thickens from about 200 feet at the northwestern extent of the Pennsylvanian to at least 600 feet in southern Illinois, but it is absent in substantial areas in both western and northern Illinois.
In Illinois the McCormick Group comprises strata of the Caseyville and Abbott Formations, from the base of the Pennsylvanian to the top of the Bernadotte Sandstone Member (fig. P-2). The McCormick Group comprises strata formerly included in the Tradewater and Caseyville Groups (Wanless, 1939; Weller, 1940).
Lithologically, this group is almost entirely detrital. It is made up of 50-60 percent massive, predominantly cross-bedded, relatively pure quartz sandstone and 40 percent or more sandy shale and siltstone. The sandstones are seldom more than 100 feet thick. A few thin, nonpersistent coals and rare fossiliferous limestones occur locally. Several of the fine-grained sandstones and a few shales are calcareous in places and contain marine invertebrate fossils, but the bulk of the units of the McCormick Group are barren of animal fossils.
KOSANKE, R. M., J. A. SIMON, H. R. WANLESS, and H. B. WILLMAN, 1960, Classification of the Pennsylvanian strata of Illinois: Illinois State Geological Survey Report of Investigations 214, 84 p.
WANLESS, H. R., 1939, Pennsylvanian correlations in the Eastern Interior and Appalachian coal fields: Geological Society of America Special Paper 17, 130 p.
WELLER, J. M., 1940, Geology and oil possibilities of extreme southern Illinois: Illinois State Geological Survey Report of Investigations 71, 71 p.
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